METHOD OF ELECTRICAL EXPLOSION OF METAL CONDUCTORS IN GASED ENVIRONMENTS (EEC)

To obtain metal nanopowders, we use the innovative EEC method. The EEC method is one of the most promising methods for producing a wide range of nanopowders of inorganic materials with high chemical activity, based on pulsed processes. This method implements a self-organization process, as in chemical synthesis, but at the same time the range of resulting nanoparticles is significantly expanded (restrictions on the physicochemical properties of the metal components forming the particle are removed) due to rapid changes in the thermodynamic parameters of the process.

The technical parameters and appearance of the machinery setup for electrical explosion of metal conductors are shown below.

The principle of operation of the EEC machinery

Basic design of the installation: 1 – reactor; 2 – section of high-voltage input and mechanical arrester; 3 – high-voltage insulator; 4 – high-voltage electrode; 5 – wire; 6 – gas flow cooler; 7 – separator; 8 – section of the feed mechanism with a wire spool and a wire length sensor; 9 – valve regulating the gas flow rate; 10 – powder collection filter; 11 – hopper (glass) for accumulating powder; 12 – shut-off valve; 13 – centrifugal fan for organizing gas movement in the cyclone; 14 – fan drive electric motor; 15 – cyclone; 16 – fabric filter; 17 – valves for cleaning the fabric filter with an external gas flow; 18 – centrifugal fan; 19 – fan drive electric motor; 20 – gas flow cooler; 21 – check valve; 22 – grounded electrode.

The electrical diagram shows the pulse current generator (PCG), consisting of a high-voltage power supply and a bank of capacitors C, which generates a high-voltage pulses. Mechanical parts are connected to the PCG via a cable entry and intended for organizing the EEC and collecting powder.

The IG (Fig. 1) charges the battery of capacitors C to the required voltage, the value of which is controlled by a kV kilovoltmeter. With the help of a switch P, C is discharged onto an exploding conductor VP located in the VK reactor. The reactor is first evacuated and filled with working gas (argon, xenon, hydrogen, etc.). The conductor explodes, current pulses I and voltage U are recorded using a current shunt R4 and a voltage divider R2, R3. The explosion products (nanopowder) are removed into the filter through window 1 by the flow of working gas, which enters through window 2. L and R1 are the circuit’s own inductance and active resistance.

During operation of the installation (Fig. 2), wire 5 is fed from section 8 in the direction of electrode 4. After the wire is advanced by the sensor to a given length, the check valve drive is turned on, which closes, cutting off reactor 1 from the reactor on the side of cooler 20. Then, under the influence of the sensor signal The mechanical arrester of section 2 is triggered, high voltage is applied to the wire and an explosion occurs. Under the influence of explosion energy, the EVP products, expanding, begin to move towards cooler section 6. Passing through the cooler, the temperature of the explosion products decreases to 20°C. The check valve opens and, under the action of the fan 18, the explosion products continue their movement in the separator 7, where large particles are separated. The wire continues to move and when the length sensor is turned on, the process repeats. Under the influence of dynamic forces formed during the explosion of the wire and the preferential circulation of the gas flow, the explosion products continue to move along the installation circuit and are deposited in the filter 10, accumulate and fall into the glass 11. Next, the gas, mainly cleared of explosion products, enters the cyclone 15 , in which particles not deposited in the filter “roll” into large, strong agglomerates and fall out into the cyclone glass 15. From the cyclone, the gas passes through a fabric filter 16, where the gas is completely purified. After filter 16, the gas passes through cooler 20 and returns to reactor 1. Fan 13 provides the required gas speed in cyclone 15. The operating frequency of the installation is at least 1.5 Hz, with a capacity for aluminum nanopowder of at least 0.2 kg/h.

The average particle size increases with increasing conductor diameter, but only up to certain values. Further, the average particle size is determined by the energy content of the explosion, and not by the diameter of the conductor. A decrease in the diameter of the conductor leads to a decrease in the average particle size, all other EEEC parameters being equal. Other factors that can changen the size of the final nano-powders include temperature and gas pressure.

Main advantages of EEC technology

• High efficiency of energy transmission, reaching 90%. In EEC technology, energy is pulsedly introduced directly into the metal volume, while energy consumption for heating the environment is relatively low.
• Possibility of flexible regulation of process parameters and, accordingly, the characteristics of the resulting nanopowders.
• Relatively small average particle size dispersion compared to other physical methods
• On the one hand, the relative stability of the properties of electroexplosive nanopowders under normal conditions, on the other hand, high activity in various chemical processes.
• The versatility of the method. In EVP technology, the only limitation is the use of conductive material of the required diameter. The method makes it possible to obtain a wide range of nano-sized materials.
• Low cost of equipment, its simplicity, small weight and size indicators.
• Low electiricty and energy requirements - This allows us to produce high volumes of nano-powders at minimal resource costs.
• There is no need to change equipment when obtaining ultrafine nanopowders of different chemical compositions.
• There is no harmful waste products produced in the manufacturing process.
• The manufacturing equipment operates at room temperature requiring no additonal heating or cooling resources.